Current sources are configured to provide an approximately constant output current to a load over a specified range of load voltages. High output impedance is an important characteristic for a current source. When a current source has a high output impedance, changes in the load conditions result in minimal changes in the output current that is provided to the load. Another important characteristic for current sources is output compliance, the range of load voltages for which an approximately constant output current is maintained.
Current sources have numerous applications. For example, current sources can be used as active loads (e.g. for differential amplifiers). Current sources can be used to bias other circuit elements. Current sources are also used in integrators and ramp generators.